This invention relates to an aluminum alloy product, and more particularly to aluminum alloy products developed for aerospace applications.
Nearly all commercial airplanes have fuselage skins made of AlClad 2024-T3. The base metal, 2024-T3 sheet, has the necessary strength and damage tolerance for aerospace applications, but suffers from susceptibility to pitting and/or intergranular corrosion attack. To compensate for that problem, the base metal is effectively isolated from the environment by a cladding layer, a paint or coating system or a combination of both.
An alcladding process involves combining a thin layer of an aluminum alloy anodic relative to 2024-T3 on both sides of 2024-T3 sheet. These layers act as a barrier and also afford galvanic protection in the 2024-T3 in case the cladding is damaged. In cases where these layers are intentionally removed by machining or chemical milling to save weight, 2024-T3 sheet may be protected with coatings and/or by anodization.
While the above protection systems are generally effective, they have some notable disadvantages. The Alclad layer contributes little with respect to strength, adds weight to the sheet and can act to initiate fatigue cracks. Other coating systems may also add weight and, if damaged, fail to protect 2024-T3 base metal. Surfaces that are anodized are brittle and can act to initiate cracks. Another disadvantage of 2024-T3 sheet is its relatively high density (0.101 lb/in.sup.3).